help! ochem questions

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1) if you have a benzyl bromide, what do you need to use to turn it into at toluene?

2) if you have butanol, how do you turn it into butane?

3) if you have two structural isomers, how can you tell which isomer is which by looking at IR? (they have the same atoms, the only thing different is that one is symmetrical and one is not)

4) when you have an epoxide, do you do a nucleophilic attack on the less hindered or more hindered side? in acid? in base?

thanks!

 

[All-Star14]

1) if you have a benzyl bromide, what do you need to use to turn it into at toluene?

2) if you have butanol, how do you turn it into butane?

3) if you have two structural isomers, how can you tell which isomer is which by looking at IR? (they have the same atoms, the only thing different is that one is symmetrical and one is not)

4) when you have an epoxide, do you do a nucleophilic attack on the less hindered or more hindered side? in acid? in base?

thanks!

1. I don't know if you can do that. You can certainly perform alkylation on the ring, but I'm not sure if you can get rid of the bromine.
2. heat/H2SO4; then H2/Pd
3. I thought IR was used only for determining functional groups
4. An epoxide would attack the less-hindered side (SN2) in base; you don't need an epoxide if you're in acid...simply protonate the leaving group to make it a better leaving group, attack the carbon attached to the leaving group, then a new bond between nucleophile and carbon forms and old bond between leaving group and carbon breaks.

 

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1) it looks like this

ph-CH2Br ---> ph-CH2D


they changed the Br to Deteurium... how? 🙁


2) Ch3Ch2CH2CH2OH ---> CH3CH2CH2CH2D

deteurium again!! how?

3) //\/\/\/\/\/ compared to /\/\/\//\/\/

how can you determine the difference between them by using IR?


4) in my notes, it seems like when you're using acid, u protonate the epoxide first, and then nuc attack at the more substituted.
but when you use a base, u attack at less substituted.

<confused>

thanks 🙂

 

[tank you]

4) in my notes, it seems like when you're using acid, u protonate the epoxide first, and then nuc attack at the more substituted.
but when you use a base, u attack at less substituted.

yea thats right, when in acidic solution, the oxygen on the epoxide gets protonated, which can then form resonance structures, and the Nu attacks the more substituted side b/c that is where the positive charge resides in the most stable carbocation. to get the idea, first draw out protonated epoxide, then move electrons around until positive charge is on the carbon bonded to most substituents, the negative Nu attacks there.

in basic solution, the Nu just attacks the least substituted side in Sn2 rxn b/c that is the fastest rxn possible.

i hope this makes sense, if not, let me know, and ill explain it to u further (orgo is my specialty)... 😀

 

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thanks... were u an ochem tutor ?

hmm do you know the other ones?

yea thats right, when in acidic solution, the oxygen on the epoxide gets protonated, which can then form resonance structures, and the Nu attacks the more substituted side b/c that is where the positive charge resides in the most stable carbocation. to get the idea, first draw out protonated epoxide, then move electrons around until positive charge is on the carbon bonded to most substituents, the negative Nu attacks there.

in basic solution, the Nu just attacks the least substituted side in Sn2 rxn b/c that is the fastest rxn possible.

i hope this makes sense, if not, let me know, and ill explain it to u further (orgo is my specialty)... 😀

 

[tank you]

1) it looks like this

ph-CH2Br ---> ph-CH2D


they changed the Br to Deteurium... how? 🙁

This is aromatic compound reaction, which are not on the MCAT anymore, well not directly anyways...

2) Ch3Ch2CH2CH2OH ---> CH3CH2CH2CH2D

deteurium again!! how?

Since deteurium is just an isotope of hydrogen, just replace the reaction where the H is added on with a D, so in this reaction, it would be:
1) H2SO4/heat
2) D2, Ni catalyst

3) //\/\/\/\/\/ compared to /\/\/\//\/\/

how can you determine the difference between them by using IR?

I have no idea, and I don't think the MCAT would require you to distinguish between terminal and internal alkenes, since there is only a tiny difference.